In mobile telecommunications networks, a user equipment (UE) may access services when outside of the geographical coverage of its home network by roaming to a visited network which has coverage in the location of the UE. This is achieved by having agreements between the home network and visited network to allow data and control signalling to pass between the networks.
For packet networks, there are two classes of roaming setups. FIG. 1 shows the nodes involved in local breakout (LBO) routing. The UE 10 is attached to a Mobility Management Entity (MME) 11, which handles all bearer and PDN connection setups for the UE. The MME 11 communicates with the HSS 16 of the home network in order to retrieve subscriber data for the UE 10. For each PDN connection, the UE is attached to a Signalling Gateway (SGW) 12, and a packet gateway (PGW). In local breakout (LBO) routing, PGW 13v and Policy Charging Rules Function (PCRF) 14v of the visited network are used, and control information is sent to the PCRF 14h of the home network (e.g. for charging and QoS purposes). Provided the service being accessed is not on the home network, no data traffic needs to travel across the home network.
The other roaming setup is home routing, as shown in FIG. 2. The UE 10 is attached to the MME 11 and SGW 12 as before. In this case, a tunnel is formed between the UE 10 and the PGW 13h of the home network. The home PGW 13h and home PCRF 14h then handle traffic for the UE 10.
A single roaming UE may use both types of routing, as multiple PDN connections may be established and each may be routed differently. For example, HTTP traffic may be home routed, while Voice over IP (VoIP) traffic may be routed via LBO.
There are advantages and disadvantages to both types of routing. For example, in LBO routing, a secure tunnel cannot be set up between the UE and the home network (as at least some nodes in the visited network need access to the packets), which prevents the use of certain services. When voice calls (e.g. over VoLTE) are home routed, it is not possible to have a seamless handover to circuit switched networks if the user moves into an area covered by legacy equipment. Also, home routed services and LBO routed services may be charged differently by the home network and/or the visited network.
LBO also allows for Alternative Roaming Providers (ARP), where a roaming provider which is not the preferred routing provider for a home network may still act as a visited network, with the roaming charging rates being determined by the ARP rather than the preferred visited network. An example of this is the proposed “euinternet” ARP.
Each gateway available to the UE is identified by an Access Point Name (APN). When the UE initially attaches to the network, it will be connected to the gateway associated with the default APN for the network, or with the gateway associated with an APN specified by the UE. For each subsequent PDN connection established by the UE, the UE may specify an APN, and the gateway associated with that APN will be used for the PDN connection. The APN details may be programmed into the UE (e.g. by the user), or configured in the UE by the network after the UE initially attaches to the network.
The process of attachment to the default APN is shown in FIG. 3. The UE 10 sends an Attach Request A1 to a Mobility Management Entity (MME) 11. The MME 11 then sends a Location Update Request A2 to a Home Subscriber Service (HSS) 16, which updates the location information of the UE and sends a Location Update Ack A3 to the MME 11. The MME 11 then sends a Create Session Request A4 to the SGW 12, specifying the default APN. The SGW 12 determines that the default APN is associated with the PGW 13, and forwards the Create Session Request A5 to the PGW 14. The PGW 13 and PCRF 14 communicate to establish the IP-CAN session A6. Once the session is established, a Create Session Response is passed from the PGW 13 to the SGW 12 (A7), and then from the SGW 12 to the MME 13 (A8). The MME 11 sends an Attach Accept A9 containing the details of the session to the UE 10, which responds with an Attach Complete A10, containing any session modifications required. The modifications are communicated to the SGW 12 by the MME 11 in a Modify Bearer Request (A11) and Modify Bearer Response (A12). The same process may be used to establish a first PDN connection to an APN other than the default APN, where the UE specifies the APN to be used in the Attach Request.
The process of establishing a subsequent PDN connection is shown in FIG. 4. The process is equivalent to that in FIG. 3, except that a Location update is not provided to the HSS 16, the Attach Request/Accept/Complete A1/A9/A10 is replaced by a PDN connectivity request/accept/complete B1/B7/B8 and the PDN connectivity request B1 may specify an APN to be connected to (which is then included in the Create Session Request B2). Signals B3 to B10 are equivalent to A5 to Alt respectively.
At present, a UE cannot reliably determine whether connecting using a specific APN would result in a home routed or LBO routed connection. The APN itself may contain some contextual clues (e.g. an APN including the name of the UE's home network operator is likely to be home routed), but there is no requirement for the APN to include such information. The UE could look up the IP address associated with the APN, and determine which operator the IP address belongs to, but this would require a large amount of extra signalling.